Without limiting the scope of the present invention, its background will be described with reference to completing a well that traverses a hydrocarbon bearing subterranean formation, as an example.
After drilling each of the sections of a subterranean wellbore, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation. Conventionally, each section of the casing string is cemented within the wellbore before the next section of the wellbore is drilled.
Once this well construction process is finished, the completion process may begin. The completion process comprises numerous steps. For example, hydraulic openings or perforations are typically created through the casing string, the cement and a short distance into the desired formation by detonating shaped charges carried in a perforating gun. The perforations allow production fluids from the subterranean formation to enter the interior of the wellbore. Once the perforations are created, however, the formation pressure must be controlled. Typically, this is achieved by loading a completion fluid into the wellbore during the completion process. The completion fluid has a density sufficient to create an overbalanced hydrostatic pressure regime at the location or locations of the wellbore perforations, thereby preventing formation fluids from entering the wellbore.
After the well is perforated, a stimulation or sand control treatment process may be performed. For example, a work string including a service tool, a gravel pack packer, a ported housing and port closure sleeve, a sealbore housings, a check valve, a wash pipe extending through the screen, a lower seal assembly and a sump packer may be run downhole. A treatment fluid, which may contain sand, gravel or proppants, is then pumped down the work string and either into the wellbore annulus, into the formation or both depending upon the desired results of the treatment process.
Following the treatment process, it remains necessary to have completion fluid in the wellbore to control formation pressure during the remainder of the completion process. Typically, this process includes tripping portions of the work string out of the wellbore and installing a production tubing string within the wellbore. The production tubing string is used to produce the well by providing the conduit for formation fluids to travel from the formation depth to the surface. In addition, the production tubing string may include various operating tools including flow control devices, safety devices and the like which regulate and control the production of fluid from the wellbore. Once the production tubing string has been installed and the completion fluid is removed from the well, production may begin.
It has been found, however, that the use of high density completion fluids to control the well during the completion process has numerous drawbacks. First, it is often desirable to perforate the well in an underbalanced hydrostatic pressure regime so that the resulting influx of formation fluids into the wellbore immediately cleans the perforation tunnels. Second, the use of high density completion fluids may result in fluid loss from the wellbore, through the perforation and into the formation during the various trips into and out of the wellbore. The introduction of this fluid into the formation may damage the formation by for, example, forming a skin near the surface of the wellbore or more critically, by promoting swelling and loss of permeability deeper within the formation. In addition, it has been found that most completion processes require the use of a drilling or workover rig during the entire completion to support equipment during the various trips into and out of the wellbore.
Therefore, a need has arisen for a system and method for completing a well that allows for an underbalanced hydrostatic pressure regime during the perforation process. A need has also arisen for such a system and method for completing a well that reduces the likelihood of fluid loss into the formation by minimizing the time it takes to complete the well and by reducing the trips into and out of the well. Further, need has arisen for such a system and method for completing a well that does not require the use of a drilling or workover rig during the treatment phase of the completion process.